My 7 year old daughter was kneed in the head today at school. She complained of a headache this afternoon. She went to sleep at 8:15 and I woke her up at 9:15 and ask her if she had a headache and she said no. Should I take her to the emergency room tonight or tomorrow?

I would keep a close eye on her, maybe wake her up again later to make sure she's ok. Generally if one gets a concussion, they say to wake the person up every so often that first night to make sure they can come to conciousness. Did she black out when she was hit? I would say if she didn't have a headache when you woke her up, just keep an eye on her. If you wake her up again and the headache's back, take her to the ER tonight.

I wouldn't go to the ER so quickly. Just keep an eye on her and make sure she's not feeling dizzy tomorrow. My son was hit in the eye with a basketball last week and had a headache for a while. Give her some tylenol if she feels pain. Kids get hit all the time. They're durable and can bounce back. Relax.

Sorry to hear about her trouble. I'll add my two cents, from experiences w/ our son. He gets headaches when he doesn't drink enough water throughout the day. This is whether he has been super active or not. Plus it seems to depend on what he has had to eat. The better his mom and I are at getting him to eat fruits/veggies the better.
May seem like obvious stuff but I know we both forget sometimes.
All the best.